Radioactive silver thiophosphate tracers for oil carrying pipe lines



United States Patent 3,305,489 RADIOACTIVE SILVER THIOPHOSPHATE TRACERS FOR OIL CARRYING PIPE LINES Bernard A. Fries, Orinda, Calif., assignor to Chevron Research Company, a corporation of Delaware No Drawing. Filed Apr. 1, 1964, Ser. No. 356,631 4 Claims. (Cl. 252-3011) This invention relates to liquid radioactive tracers and methods for their preparation and pertains more particularly to a stable oil soluble tracer consisting essentially of a thiophosphate prepared from radiosilver-llO that is of specific utility in tracing the Bow of oils through pipe lines.

In the operation of long pipe lines through which successive batches of oil and liquid hydrocarbon products are passed, it is essential to be able to distinguish the interfaces between different products so that they may be separated at their points of take-off or delivery. A suitable method that has been developed Consists in the introduction into the interface between successive different products of a small quantity of an oil-soluble liquid carrying a radioisotope that can be detected outside of the pipe line at any point along its length. Usually the isotope is chosen to be a gamrna-cmitter, and compounds of radioactive antimony and the like have been employed as described in Patent No. 2,706,254 of R. C. Mithotf and D. E. Hull. It has also been proposed to prepare and to utilize oil-soluble sulfonates of cesium isotopes, C8 and Cs as exemplified in my Patent No. 2,835,699.

Unfortunately, these prior oil-soluble radioactive tracers are not satisfactory in use, for example, when added as tracers to the interface of diesel fuel and like oily liquids.

Therefore, it is an object of the present invention to provide an improved oil-soluble and water-insoluble radioactive liquid tracer composition and also a composition which is stabilized against reactive components sometimes contained in the oily liquid being transported through the pipe lines. It is also an object to provide a method for preparing these improved radioactive tracer compositions that will be safe and convenient to use.

Another object is to provide as a new and useful prodnot, a stable oil-soluble thiophosphate of radiosi1ver-110 These and other objects and advantages will be further apparent from the following specification which describes the improved product and procedures for preparing it.

The radioactive isotope of silver, Ag is available to qualified users from Oak Ridge National Laboratory of the United States Atomic Energy Commission as a solution of the nitrate salt or as the solid metal having a very high specific radioactivity and thus requiring shielded handling as is Well known in this art. The final product also requires suitable monitoring procedures and equipment for safe storage and utilization. The isotope Ag has a half life of about 250 days and emits principally gamma rays of 0.9, 1.4 and 1.5 m.e.v. energy. Such emission is of suitable magnitude to penetrate the steel wall of a pipe line and be detected outside of the pipe by single or multiple units of gamma ray detectors. Hence, the oil-soluble radiosilver-lltl thiophosphates of this invention are very desirable for tracer applications such as in pipe lines.

The radioactive cesium sulfonates of my Patent No. 2,835,699 are quite stable in gasoline or other light pipe line products but are occasionally unstable in pipe line oils. The new oil-soluble radiosilver-llO thiophosphate tracers are especially resistant to extraction or loss from solution in pipe line oils heavier than gasolines, particularly when transported in pipe lines containing small amounts of water and reactive materials which tend to promote the extraction and/ or exchange with other ions.

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Patented Feb. 21, 1967 Thus in a 40 mile pipe line transporting diesel fuels con taining detergent additives, C5 sulfonate tracer disappears from the flowing product before it reaches the end of the line whereas an Ag thiophosphate of the present invention remains in the product as a useful indicator. It is believed that the low susceptibility of the Ag thiophosphate to ion exchange and extraction is due to the Ag-S linkage which is essentially covalent and nonpolar.

The radioactive tracers are and must be prepared with care, centrifuging and washing of precipitates being avoided to minimize the radioactive hazard. Consequently, chemical procedures involving a minimum number of chemical operations are desirable.

Example 1 In this example, 172 milligrams of radiosilver-lltl containing 190 me. was received in 13.9 ml. of 0.8 N nitric acid. The excess nitric acid was removed by evaporating to dryness. Ammonia hydroxide was added to the dry residue to convert the nitrate to the hydroxide and the excess ammonium hydroxide removed by evaporating to dryness. The resulting residue of silver oxide and ammonium nitrate was then heated to about F. and stirred with 22 grams of dicetylphenyl thiophosphoric acid which is an oily liquid available from the reaction of P 8 and the cetylphenol (prepared as an alkylate of phenol and propylene polymer of about 16 carbon atoms). The resulting mixture wa dissolved in petroleum thinner forming a clear, bright solution which remained stable indefinitely on storage. When so prepared for use in a products pipe line, the oil-soluble radiosilver1l0 thiophosphate tracer composition had a thiophosphate concentration of 55 mg./ml. and an Ag concentration of 0.34 mc./ml.

The oil-soluble thiophosphoric acid can contain other oil-solubilizing alkaryl, aliphatic or like groups, it only being essential that the group confer adequate oil solubility and the resulting tracer have the radiosilver-llO' in a thiophosphate Ag-S linkage.

Example 2 In this example, 2.0 grams of radiosilver-llO containing about 1000 me. was dissolved in 10 ml. of 6 N nitric acid, after which the excess acid was removed by evaporating to dryness. The dry silver nitrate residue was mixed with 1 ml. of water and then 26 grams of diethylphenyl thiophosphoric acid which had been neutralized with a stoichiometric amount of an oil-soluble amine, namely, the reaction products of tetraethylene pentamine and polyisobutylene succinic anhydride having about 65 carbon atoms in the polyisobutylene group. On stirring for several hours, the silver nitrate completely reacted and there was no appreciable residue. The resulting product was dissolved in petroleum thinner to give a clear solution having an Ag concentration of 3 ml./mc. The product was stable and remained so indefinitely. Also, the minimum number of chemical operations were used in preparing the product. Complete recovery of radioactivity can be obtained by reworking any residues. The addition of the oil soluble amine and its reaction product with excess thiophosphoric acid served to stabilize the silver thiophosphate. Other reaction products of alkenyl succinic anhydride and alkylene amines, as well as other oil-soluble amines, can be used for this purpose. However, when a lower molecular weight amine such as aniline was employed in a stoichiometric amount with the thiophosphoric acid the reaction with the silver nitrate proceeded smoothly but an undesirable oil insoluble precipitate of aniline nitrate was formed. Further, when the process was repeated without an amine being present and the silver nitrate stirred with the thiophosphoric acid, considerable heat was evolved, N0 liberated, and decomposition occurred.

When the preferred product of Example 2 was introduced as an interface tracer into a diesel fuel product containing detergent additives, the product remained stable and active after passing through more than 500 miles of pipe line. The present oil soluble thiophosphates of Ag as compared to Sb compounds, have longer half lives and hence can be prepared and shipped for use at less frequent intervals.

I claim:

1. A radioactive tracer consisting essentially of a stable oil soluble Ag thiophosphate.

2. A radioactive tracer according to claim 1 in which the tracer is stabilized with an oil soluble amine.

3. A radioactive tracer consisting essentially of a thiophosphate obtained by reacting an oil-soluble thiophosphoric acid with an inorganic compound of Ag 4/1964 Beerbower et a1. 250106 7/1964 Dvorkovitz et al. 252-30L1 OTHER REFERENCES Van Wazer, Phosphorus and its Compounds, vol. I, Interscience Publishers, Inc., New York, 1958, pp. 824-5.

CARL D. QUARFORTH, Primary Examiner.

BENJAMIN R. PADGETT, Examiner.

L. A. SEBASTIAN, Assistant Examiner. 

1. A RADIOACTIVE TRACER CONSISTING ESSENTIALLY OF A STABLE OIL SOLUBLE AG110M THIOPHOSPHATE. 